1. Field of the Invention
The present invention relates to a vibration damper having a piston cylinder with a cylinder, a piston connected to a piston rod axially movably arranged in the cylinder, and a stop spring which is compressed after a piston rod of the vibration damper reaches a defined stroke position and which defines a radially inner space connected to a working space in said cylinder.
2. Description of the Related Art
DE 78 02 898 U1 discloses a vibration damper with a stop spring in the form of a circular elastomeric ring, which is concentric to a piston rod inside a damping medium-filled working space on the piston rod side of the vibration damper. As soon as a defined stroke position is reached, the stop spring is clamped by a stop on the piston rod side against an end surface of a piston rod guide facing the working space. When the stop spring is compressed, the volume of the damping medium present in the annular space between the piston rod and the stop spring is pushed radially outward through transverse openings. These transverse openings, however, are also axially clamped, and their cross section is thus reduced. To ensure that damping medium can continue to escape from the annular space, the stop spring has radial channels in its end surfaces; these channels connect the annular space to the working space on the piston rod side. At an increased level of compression, however, these radial channels can also be closed by the displacement or deformation of the entire stop spring. Thus the damping medium can escape from the annular space only in the direction toward the piston rod guide Experiments have shown that this effect does not lead to any damage in the case of a vibration damper of the two-tube type. Two-tube vibration dampers such as those known from U.S. Pat. No. 4,287,970 have a side channel between a piston rod bush and a piston rod seal. Oil carried along on the piston rod can escape through this side channel to a compensating space. This side channel can then also be used by the damping medium to escape from the annular space of the stop spring. This possibility is not available in a vibration damper of the single-tube type, the compensating space of which is frequently located downstream from the working space on the side of the piston facing away from the piston rod. Under certain conditions, therefore, damping medium can emerge in the gap between the stop spring and the piston rod. It has also been found that the previously described problem occurs primarily in the case of comparatively long stop springs. The use of short stop springs, however, does not represent a genuine solution, because it is necessary to maintain a specific damping force characteristic.
A stop spring with a closed, ring-shaped body as a spring element and metal angular rings at one end, which slide on the piston rod, is known from U.S. Pat. No. 4,527,674. These angular rings have short webs on the axial end surfaces, so that radial discharge channels are present when the end surface rests against, for example, the piston rod guide. The discharge channels are guaranteed to remain open. The metal angular rings, however generate noise when they strike the piston rod guide, and this interferes with passenger comfort.